Single-screw compressors have been used in the art as compressors for compressing refrigerant or air. For example, Japanese Published Patent Application Nos. 2002-202080 and 2001-065481 disclose a single-screw compressor including a screw rotor and two gate rotors.
The single-screw compressor will be described. In the single-screw compressor, a screw rotor is accommodated in a casing. The screw rotor is formed generally in a cylindrical shape with a plurality of helical grooves cut in the outer circumferential portion thereof. Each gate rotor is formed generally in a flat plate shape and arranged beside the screw rotor. The gate rotor is provided with a plurality of rectangular plate-shaped gates arranged in a radial pattern. The gate rotor is installed in such an orientation that the rotation axis thereof is perpendicular to the rotation axis of the screw rotor, with the gates meshed with the helical grooves of the screw rotor. In a typical single-screw compressor, a gate rotor is formed as a flat-plate shape resin, and is attached to a metal supporting member having a rotation shaft portion.
In the single-screw compressor, the screw rotor and the gate rotor are accommodated in a casing, and a compression chamber is formed by the helical grooves of the screw rotor, the gates of the gate rotors, and the inner wall surface of the casing. As the screw rotor is rotated by an electric motor, etc., the gate rotor is rotated by the rotation of the screw rotor. Then, the gates of the gate rotors relatively move from the start end (the suction side end portion) to the terminal end (the discharge side end portion) of a meshing helical groove, thereby gradually reducing the volume of the closed compression chamber. As a result, the fluid in the compression chamber is compressed.
In a single-screw compressor in operation, the front surface side of a gate meshed with a helical groove of the screw rotor serves as a compression chamber in the compression phase (i.e., a compression chamber in a closed state), and the back surface side of the gate serves as a compression chamber in the suction phase (i.e., a compression chamber that communicates with the suction side). The pressure of a compressed fluid acts upon the front surface of a gate meshed with a helical groove of the screw rotor, and the pressure of an uncompressed fluid acts upon the back surface thereof. Therefore, a gate meshed with a helical groove of the screw rotor receives a force acting thereupon in such a direction as to push the gate to the back surface side thereof. On the other hand, the gate is supported by a supporting member from the back surface side thereof. Thus, the supporting member receives a force that pushes the gate to the back surface side, and the gate will not therefore be damaged by receiving a fluid pressure in the compression chamber.